1. Field
The present disclosure relates generally to simulating variation in manufacturing, and in particular to designed objects. Still more particularly, the present disclosure relates to a method and apparatus of simulating surfaces of a structure.
2. Background
When parts and assemblies are manufactured, variances may occur in the dimensions of manufactured parts or the assembly of parts. Engineers attempt to consider and account for such variances when designing the parts and assemblies by designing each measurement within a part or assembly with a tolerance.
A tolerance allows a manufactured part to be considered acceptable if all the variation in measurements on the manufactured part fall within the chosen range of tolerance. The tolerance may be chosen by the engineer or other actor in the engineering process based on a balance between engineering requirements and manufacturing costs. As tolerances decrease, that is, the requirement for the manufactured part become more stringent, manufacturing costs increase. Manufacturing costs may increase because the manufacturer will require more precise tooling to make parts that will meet the stringent tolerance requirements. Manufacturing costs may also increase because more manufactured parts will be deemed unacceptable during the manufacturing process.
For example, an engineer may be designing a door for an airplane. It is an engineering requirement that the door make a tight seal with the fuselage. The engineer must, however, keep manufacturing costs as low as possible. Therefore, the engineer may specify a tolerance for the measurements, that is, that all the measurements for the edges around the door may vary by a certain distance in any direction. When the door is built, this tolerance allows the builder to accept parts that have edges with measurements that are not exact to the specified design, but will still meet the requirement that the door make a tight seal with the fuselage.
Engineers use a language called Geometric Dimensioning and Tolerancing (GD&T) to describe the tolerance of measurements in their design. Engineers may send part designs including Geometric Dimensioning & Tolerancing for the various measurements of a part to an analyst to determine approximately what percent of parts or assemblies of parts manufactured with the given tolerances will fail to meet the engineering requirements.
To perform the analysis, the analyst may use a computer to recreate the design of the part, including specified measurements and tolerances in virtual space. The analyst then simulates the manufacturing of the parts with the specified tolerance range. The analyst then reaches a determination on the approximate percentage of parts or assemblies that would not meet the engineering specification.
Currently, however, the simulation does not accurately represent tolerances that are specified by the engineer as a rate of change for a surface. The rate of change may be specified over a particular distance. An example is 0.005/5, that is, the measurement may vary 0.005 inches in a positive or negative direction over a run of 5 inches. Since the rate of change cannot be accurately represented in the simulation, the simulation returns inaccurate results for parts or assemblies that do not meet the specification. An inaccurately high result may cause an engineer to redesign parts unnecessarily, while an inaccurately low result may cause an unexpectedly high number of rejected parts when the part is actually manufactured. In either case, overall product costs are higher than if the simulation accurately represented rate of change tolerances.
Thus, it would be advantageous to have a method, a computer program product, and an apparatus that takes into account one or more of the issues discussed above, as well as possibly other issues.